Digital radiography is achieving a growing acceptance as an alternative to photographic-based imaging technologies that rely on photographic film layers to capture radiation exposure to produce and store an image of a subject's internal physical features. With digital radiography, the radiation image exposures captured on radiation sensitive layers are converted, pixel by pixel, to electronic image data which is then stored in memory banks for subsequent read-out and display on suitable electronic image display devices. One of the driving forces in the success of digital radiography is the ability to rapidly communicate stored images via data networks to one or more remote locations for analysis and diagnosis by radiologists without the delay caused by having to send physical films through the mail or via couriers to reach the remotely located radiologists.
Of critical importance in digital radiology technology is the need to create high-resolution electronic image data that is preferably at least as high in resolution as its photographic based counterpart. The amount of image data that must be processed and the consequent frequency bandwidth of the signal processing circuits needed to achieve the necessary data processing within a given time frame is a multifunctional consideration based on such factors as the size of each pixel, the pixel array size, the maximum range of pixel exposure to be detected, and detectable exposure density gradients of each pixel.
FIGS. 1-3 illustrate a conventional digital radiography system 10 which includes a digital radiography panel 12 having a substrate on which is formed a radiographic sensor layer 14 which generates electrons in response to impinging radiation e.g. X-rays. The term X-ray is used for convenience throughout this description and in the appended claims. However, it will be understood that the invention is useful in digital radiography employing other forms of radiation and, thus, the term X-ray herein shall be interpreted to cover such other forms of radiation as are used. The radiation-generated electrons are captured by capacitors 16 which are arrayed on substrate 15 in rows and columns and which thereby define discrete pixel sites 17. After exposure of a subject, the capacitors are addressed, a row at a time, by switching control circuit 18 via conductors 19 and solid state switches 20 to transfer the respective charge values via read-out lines 22 to external electronics circuitry 24, which includes preamplifiers and analog-to-digital (A:D) converters, to convert the charge values to voltage values and then into digital numeric data, typically 14 bits per pixel. Once digitized, the data is transferred to suitable digital image processor circuits 25 and applied to image display 26 for viewing. The data may also be stored in data storage memory 28 and/or sent to a network 29 for communication to a remote site for viewing.
The read-out of millions of pixel charge values involves use of high bandwidth analog electronics and also exposes individual pixel values to cross talk from adjacent pixels. As previously mentioned, the high bandwidth analog electronics increases noise in the analog signals. Additionally, cross talk serves to contaminate each pixel value.
There is a need therefore, for a digital radiography panel system that avoids the problems associated with existing panel systems utilizing analog signal read-out. The present invention serves that need.